1. Field of the Invention
The present invention relates to an image processing method used in display of a video image in a display apparatus capable of setting a vertical synchronizing frequency (a time interval at which the display screen is updated).
2. Description of the Related Art
Different devices including a monitor display, an inkjet printer, and an offset printer have different color reproduction ranges. Accordingly, color management systems (hereinafter referred to as CMSs) are proposed, which perform color management so that reproduced video images do not have different colors in different devices (for example, refer to Bruce Fraser, Chris Murphy, Fred Bunting, 2005, “Color Management—Riron to Jissen (Color Management—Theory and Practice)”, Kabushiki-gaisha Vanfu, pp. 81 to 85).
The CMS converts the color space so that RGB values or CMYK values transmitted from a video input device (for example, a camera) are reproduced in the same colors in any display apparatus (for example, a display device).
However, the luminance and color of a video image can be varied depending on a vertical synchronizing frequency set in the display apparatus.
The vertical synchronizing frequency represents the number of times a display device updates (rewrites) the display screen per second. The vertical synchronizing frequency is also called a vertical scanning frequency or a refresh rate and is represented in hertz. In other words, the luminance and color on a display screen can possibly be varied depending on the time interval at which the display apparatus updates the display screen. For example, the vertical synchronizing frequency set for the display apparatus can be used to vary the time interval at which the display screen is updated.
FIG. 9 is a graph showing an example of the relationship between the luminance and the gradation when video images are displayed in a cathode ray tube (CRT) display in response to the same video signal at two different vertical synchronizing frequencies. A line A in FIG. 9 shows the luminance relative to the gradation when the vertical synchronizing frequency is equal to 60 Hz. A line B in FIG. 9 shows the luminance relative to the gradation when the vertical synchronizing frequency is equal to 120 Hz.
As shown in FIG. 9, the luminance of a video image can be varied depending on the vertical synchronizing frequency.
FIG. 10 shows Lab values on an a-b plane, which are measured when video images are displayed in a CRT display in response to the same video signal at the vertical synchronizing frequencies shown by the lines A and B in FIG. 9. As shown in FIG. 10, the a-b value of a reproduced video image can be varied depending on the vertical synchronizing frequency.
As described above, a video image can be reproduced in different colors and luminances at different vertical synchronizing frequencies (time intervals at which the display screen is updated) of the display apparatus.